1. Field of the Invention
The present invention relates to preventing acoustic shock in voice communication systems.
2. Background Art
Exposure to noise can cause various health problems including permanent hearing loss, temporary hearing loss, tinnitus, headaches, depression, increased sensitivity to loud noises, and the like. The risk of injury and the extent of any resulting injury are functions of the intensity of noise levels, the length of exposure, the type of noise, and the sensitivity level of the person exposed. Acoustic shock can occur due to a sudden or unexpected noise or due to prolonged exposure to noise. Various types of workers are susceptible to injury from acoustic shock, including telephone operators, telemarketers, technical support personnel, and the like, who spend a great many hours using a telephone. Other activities that expose a person to prolonged sound sources may also be susceptible.
A telephone near-end user can experience unpleasant sounds resulting in acoustic shock when an outgoing call inadvertently connects with a fax machine, modem, or similar device. Acoustic shock can also occur when a far-end user hits a telephone button, generating a DTMF signal. Other sources of acoustic shock can include noise coupled into a telecommunication system from natural or man-made sources, failure of telecommunications equipment, and the like.
Different standards exist for limiting acoustic pressure in headsets and handsets. The North American A-weighted curves are based on a 90 dBA eight hour time weighted average free field noise exposure limit. In other words, a user cannot be subjected to more than 90 dBA noise level during an eight hour period. The CERN standard permits an 85 dBA exposure limit over eight hours. Both standards are measured at the ear reference point (ERP). Both standards permit higher noise levels for shorter periods of time. In calculating exposure, acoustic pressure values may be corrected according to several factors including non-occupational exposure, whether the noise was received from a headset or a handset, signal bandwidth, and the like.
What is needed is to prevent acoustic shock, as much as possible, without excessively inhibiting desirable signal components such as speech, dial tones, ring tones, and the like. Acoustic shock should be prevented without the use of a computationally intensive algorithm, permitting inexpensive implementation within handsets, headsets, and other telecommunications equipment.